The purpose of this investigation is to evaluate a new restorative hybrid type restorative material (EXL 324) and to compare its wear characteristics with Z100 (3M Co.) Restorative material presently available in the dental market and having well characterized wear data. Ten Z100 restorations and twelve experimental materials were randomly placed in the posterior teeth of six M. fascicularis monkeys. The two materials were clinically evaluated at one month and impressions taken at that time to measure the amount of wear that had occurred directly on the plastic casts of the restored teeth. The casts are evaluated for wear by two evaluators by viewing through a dissecting microscope in a double blind study. Further evaluations of the materials will be made at three months and at six monthly intervals thereafter. Some wear was noted on the experimental materials EXL 325 after one year but restorations were still serviceable.